1. Field of the Invention
The present invention relates to a blast tuyere of a blast furnace such as a blast furnace for manufacturing iron, a blast furnace for manufacturing nonferrous metals, and a cupola.
2. Related Art
A blast tuyere (referred to as a tuyere hereinafter) of a blast furnace is usually installed in the vicinity of the boundary between the belly and the bottom of the blast furnace, and in many cases a portion of 400-600 mm length at the tip side of the tuyere is projected into the blast furnace. A cool blast or a hot blast is blown from the tip portion (nose) to the inside of the blast furnace. The highest temperature of the hot blast reaches 1250.degree. C., and the highest temperature of the flame in front of the tuyere rises up to 2450.degree. C. Moreover, the interior of the furnace is in the state that pig iron melted at 1500.degree. C. or higher and slag are dropped.
Under such a severe temperature condition, any tuyere must keep its original form and simultaneously cause a hot blast to continue to blow. In the present technology, therefore, a tuyere is made of highly pure copper (Cu) having a high heatproof temperature and a good heat conductivity. In addition, a circular flowing route for cooling-water is formed in the body of the tuyere, and water is permitted to flow in the circular flowing route at a high flowing speed to cool the tuyere, as is known in Japanese Utility Model Application Laid-Open No. 3-29310, as well.
Since the birth of a blast furnace, however, damage of tuyeres has come into question to be solved. In other words, when the method for cooling tuyeres is improved, the operation conditions of blast furnaces become more severe accordingly so as to induce damage of the tuyeres, and that this predicament has been repeated. The following will broadly describe the history about the improvement in tuyeres of blast furnace.
About 70 years ago, Mr. Hirakawa stated that the cause of the damage of a tuyere is "superheat by contact between the tuyere and a hot metal", and reported, as a countermeasure against the cause, that aluminum (Al) is satisfactory as a material of a tuyere since "a material having a large thermal resistance (thickness/thermal conductivity) and a smooth surface is suitable for the material of the tuyere" and that "an Al tuyere is superior to Cu in workability (light weight) as well as resistance against tuyere failure" (see "Iron and Steel" Vol. 16(1930) No. 6, p. 595). However, Al tuyeres were frequently damaged. Thus, Cu tuyeres have been used since about 1950.
Since about 1960, blast furnace operation has been corresponding to the fact that furnaces have become large-scale. Thus, in those days high pressure operation, high temperature blast, oil injection and oxygen enrichment started. Furthermore, in about 1980, pulverized coal injection started. With such high productivity operation, temperature of the space in front of a tuyere was raised by a rise in temperature of hot blast and injection of a burning aid agent and oxygen. Moreover, the drop amount of hot metal or slag was remarkably increased by improvement in productivity. Based on such causes, thermal load on the tuyere was greatly increased. As a result, tuyere failure frequently occurred again. Once a tuyere is damaged, it is essential that blowing-down is carried out and the tuyere is exchanged. Thus, the reduced amount of production is larger. In the worst case, it is feared that an accident resulting in injury or death happens by serious damage of the tuyere and furnace operation becomes in a bad condition or impossible by invasion of tuyere-cooling-water into a furnace. Accordingly, various improvements have been made, from the standpoint of necessity of preventing tuyere failure.
Incidentally, tuyere failure is classified into 7 types, that is, failure in the upper portion, the two side portions and the lower portion of the outer surface of the tuyere body; the upper portion, the two side portions and the lower portion of the tuyere nose; and the inner surface of the tuyere body.
Recent improved countermeasures against such failure are as follows:
(1) a two chamber type tuyere structure wherein a cooling chamber (for a body chamber) of a tuyere body, and a front cooling chamber and a rear cooling chamber (each of which is for a nose chamber) of a tuyere nose are separately disposed inside the trunk of the tuyere (Japanese Patent Application Publication No. 60-55562), (2) a spiral tuyere structure for causing water to flow from the body of a tuyere trunk, through an outer cooling-water chamber, a spiral passage, and a front circular passage, to an inner cooling-water chamber and further to be discharged from the body of the tuyere trunk, so as to raise the speed of the cooling-water, in particular, at a tuyere nose(Japanese Patent Application Publication No. 51-19802), (3) hard-facing structure for preventing wear at a tuyere nose (Japanese Utility Model Application Laid-Open No. 55-124446), (4) alloy padding structure for raising melting temperature (Japanese Utility Model Application Laid-Open No. 4-131639), (5) inner face ceramic lining processing for preventing the inner face of a tuyere from being failed and worn (Japanese Patent Application Publication No. 6-60333), and the like. At present improved means comprising a single from them or a combination of them are adopted.
As a result, the failure in the inner face of a tuyere hardly arises by the inner face ceramic lining processing. Furthermore, the frequency of failure in the nose of the tuyere can greatly be reduced by both cooling-water having high pressure and speed and the hard-facing.
However, the frequency of failure in the outer surface of the tuyere body, particularly the upper portion of the outer surface, is not reduced even by such improved means. This is because the drop of a hot metal of 1500.degree. C. or more falls, from the upper part of a furnace, directly onto the outer surface of the tuyere body, so that the drop contacts Cu constituting the tuyere and causes the Cu to be melted.
Of course, in this case, even if hot melt slag of 1500.degree. C. or more drops from just above the tuyere, the tuyere is not damaged in the case wherein the upper surface of the tuyere body is not heated to the melting point of Cu or higher. Furthermore, even if the fluid surface level of the hot metal or slag rises so that the fluid of 1500.degree. C. or higher contacts the lower surface of the tuyere body, the tuyere is not damaged in the case wherein the tuyere body is not heated to the melting point of Cu or higher. At present, however, there is not realized a cooling means for, even if the hot metal or slag contacts the tuyere directly, keeping the temperature of the contacted portion of the tuyere below the melting point. Thus, there remains a problem that the frequency of failure in the outer surface of the tuyere body is still high.